1. Field of the Invention
The present invention relates generally to fluid delivery devices. More particularly, the invention concerns an improved apparatus for infusing medicinal agents into an ambulatory patient at specific rates over extended periods of time.
2. Discussion of the Invention
Many medicinal agents require an intravenous route for administration thus bypassing the digestive system and precluding degradation by the catalytic enzymes in the digestive tract and the liver. The use of more potent medications at elevated concentrations has also increased the need for accuracy in controlling the delivery of such drugs. The delivery device, while not an active pharmacologic agent, may enhance the activity of the drug by mediating its therapeutic effectiveness. Certain classes of new pharmacologic agents possess a very narrow range of therapeutic effectiveness, for instance, too small a dose results in no effect, while too great a dose results in toxic reaction.
In the past, prolonged infusion of fluids has generally been accomplished using gravity flow methods, which typically involve the use of intravenous administration sets and the familiar bottle suspended above the patient. Such methods are cumbersome, imprecise and require bed confinement of the patient. Periodic monitoring of the apparatus by the nurse or doctor is required to detect malfunctions of the infusion apparatus.
Devices from which liquid is expelled from a relatively thick-walled bladder by internal stresses within the distended bladder are well-known in the prior art. Such bladder, or "balloon" type, devices are described in U.S. Pat. No. 3,469,578, issued to Bierman and in U.S. Pat. No. 4,318,400, issued to Perry. The devices of the aforementioned patents also disclose the use of fluid flow restrictors external of the bladder for regulating the rate of fluid flow from the bladder.
The prior art bladder type infusion devices are not without drawbacks. Generally, because of the very nature of bladder or "balloon" configuration, the devices are unwieldy and are difficult and expensive to manufacture and use. Further, the devices are somewhat unreliable and their fluid discharge rates are frequently imprecise.
The apparatus of the present invention overcomes many of the drawbacks of the prior art by eliminating the bladder and making use of recently developed elastomeric films, expandable foams and similar materials, which, in cooperation with a base defines a fluid chamber that contains the fluid which is to be dispensed. The elastomeric film membrane or the expandable foam member controllably forces fluid within the chamber into fluid flow channels provided in the base.
The elastomeric film materials used in the apparatus of the present invention, as well as various alternate constructions of the apparatus, are described in detail in U.S. Pat. No. 5,205,820 issued to the present inventor. Therefore, U.S. Pat. No. 5,205,820 is hereby incorporated by reference in its entirety as though fully set forth herein. Co-pending U.S. Ser. No. 08/129,693 filed by the present inventor on Sep. 29, 1993 also describes various types of expandable cellular elastomers and elastomeric foams used in making the expandable member of various physical embodiments of the invention. This co-pending application is also hereby incorporated by reference in its entirety as though fully set forth herein.
The apparatus of the present invention can be used with minimal professional assistance in an alternate health care environment, such as the home. By way of example, devices of the invention can be comfortably and conveniently removably affixed to the patient's body and can be used for the continuous infusion of antibiotics, hormones, steroids, blood clotting agents, analgesics, and like medicinal agents. Similarly, the devices can be used for I-V chemotherapy and can accurately deliver fluids to the patient in precisely the correct quantities and at extended microfusion rates over time.
One of the embodiments of the invention described in Continuation-In-Part application Ser. No. 08/129,693 comprises a generally circular base assembly and a stored energy means provided in the form of a thin, generally circular shaped, pre-stressed distendable elastomeric membrane which cooperates with the base assembly to form a fluid reservoir. Superimposed over the base assembly is a rigid, distendable membrane engagement means which provides an ullage within the reservoir.
The embodiments of the invention described herein comprise improvements to the devices described in U.S. Pat. No. 5,205,820 and in U.S. Ser. No. 08/129,693. More particularly, the inventions described herein are directed toward providing novel fluid delivery devices which are extremely low profile and are eminently capable of meeting the most stringent of fluid delivery tolerance requirements. In this regard, medical and pharmacological research continues to reveal the importance of the manner in which a medicinal agent is administered. The delivery device, while not an active pharmacological agent, may enhance the activity of the drug by mediating its therapeutic effectiveness. For example, certain classes of pharmacological agents possess a very narrow dosage range of therapeutic effectiveness, in which case too small a dose will have no effect, while too great a dose can result in toxic reaction. In other instances, some forms of medication require an extended delivery time to achieve the utmost effectiveness of a medicinal therapeutic regimen.
By way of example, the therapeutic regimens used by insulin-dependent diabetics provide a good example of the benefits of carefully selected delivery means. The therapeutic object for diabetics is to consistently maintain blood glucose levels within a normal range. Conventional therapy involves injecting insulin by syringe several times a day, often coinciding with meals. The dose must be calculated based on glucose levels present in the blood. If the dosage is off, the bolus administered may lead to acute levels of either glucose or insulin resulting in complications, including unconsciousness or coma. Over time, high concentrations of glucose in the blood can also lead to a variety of chronic health problems, such as vision loss, kidney failure, heart disease, nerve damage, and amputations.
A recently completed study sponsored by the National Institutes of Health (NIH) investigated the effects of different therapeutic regimens on the health outcomes of insulin dependent diabetics. This study revealed some distinct advantages in the adoption of certain therapeutic regimens. Intensive therapy that involved intensive blood glucose monitoring and more frequent administration of insulin by conventional means, i.e., syringes, throughout the day saw dramatic decreases in the incidence of debilitating complications.
The NIH study also raises the question of practicality and patient adherence to an intensive therapy regimen. A bona fide improvement in insulin therapy management must focus on the facilitation of patient comfort and convenience as well as dosage and administration schemes. Basal rate delivery of insulin by means of a convenient and reliable delivery device over an extended period of time represents one means of improving insulin management. Basal rate delivery involves the delivery of very small volumes of fluid (1-3 mL.) over comparatively long periods of time (18-24 hours). As will be appreciated from the discussion which follows, the apparatus of the present invention is uniquely suited to provide precise fluid delivery management at a low cost in those cases where a variety of precise dosage schemes are of utmost importance.
In those embodiments of the invention described in U.S. Pat. No. 5,205,820 issued to the present inventor and incorporated herein by reference, the fluid delivery apparatus components generally included: a base assembly; an elastomeric membrane serving as a stored energy means; fluid flow channels for filling and delivery; flow control means; a cover; and an ullage, which comprised a part of the base assembly. The ullage in these devices typically comprises a semi-rigid structure having flow channels leading from the top of the structure through the base to inlet or outlet ports of the device.
In the rigid ullage configuration, the stored energy means of the device must be superimposed over the ullage to form the fluid-containing reservoir from which fluids are expelled at a controlled rate by the elastomeric membrane of the stored energy means tending to return to a less distended configuration in a direction toward the ullage. With these constructions, the stored energy membrane is typically used at high extensions over a significantly large portion of the pressure-deformation curve (FIG. 1A).
Elastomeric membrane materials suitable for use as the stored energy means must possess certain physical characteristics in order to meet the performance requirements for a fluid delivery apparatus. More particularly, for good performance, the elastomeric membrane material must have good memory characteristics under conditions of high extension; good resistance to chemical and radiological degradation; and appropriate gas permeation characteristics depending upon the end application to be made of the device.
Once an elastomeric membrane material is chosen that will optimally meet the desired performance requirements, there still remain certain limitations to the level of refinement of the delivery tolerances that can be achieved using the rigid ullage configuration. These result primarily from the inability of the rigid ullage to conform to the shape of the elastomeric membrane near the end of the delivery period. This nonconformity can lead to extended delivery rate tail-off and higher residual problems when extremely accurate delivery is required. For example, when larger volumes of fluid are to be delivered, the tail-off volume represents a smaller portion of the fluid amount delivered and therefore exhibits much less effect on the total fluid delivery profile, but in very small dosages, the tail-off volume becomes a larger portion of the total volume. This sometimes places severe physical limits on the range of delivery profiles that may easily be accommodated using the rigid ullage configuration.
An acceptable elastomeric membrane material candidate for the rigid ullage configuration must also be drug compatible as is typically in contact with any drug containing fluid disposed within the reservoir. Many currently available elastomeric membrane materials, due to their chemical composition or means of manufacturing, are not drug compatible. This compatibility restriction, combined with strict physical requirements, results in further limitation of available selections for the candidate elastomeric material for use in devices embodying a rigid ullage structure.
As will be better appreciated from the discussion which follows, the apparatus of the present invention provides a unique and novel improvement for a disposable dispenser of simple but highly reliable construction that may be adapted to many applications of use. A particularly important aspect of the improved apparatus is the incorporation of a conformable ullage made of yieldable materials, the conformable ullage uniquely conforms to the shape of elastomeric membrane as the membrane returns to its less distended configuration. This novel construction will satisfy even the most stringent delivery tolerance requirements and will elegantly overcome the limitations of materials selection encountered in devices embodying the rigid ullage construction. Another significant advantage of the novel ullage construction is that the ullage can be located either between the base and the fluid to be delivered, or alternatively, can be located between the elastomeric membrane and the fluid to be delivered. Further, a plurality of subreservoirs can be associated with a single ullage thereby making it possible to incorporate a wide variety of delivery profiles within a single device.
Although the infusion devices described in U.S. Pat. No. 5,205,820 and in U.S. Ser. No. 08/129,693 are very low profile devices, the devices of the inventions described herein are designed in a manner so that they can be of even a lower profile thereby making them ideally suited for use in dispensing medicinal agents such as insulin and the like.